1. Field of the Invention
The present invention relates to a high-frequency switch module that transmits and receives a plurality of types of high-frequency signals by connecting a common terminal to one of a plurality of individual terminals by using a semiconductor switch.
2. Description of the Related Art
Various types of high-frequency switch modules for transmitting and receiving a plurality of high-frequency signals by using a common antenna have been devised. In such a high-frequency switch module, there is a case in which a switch IC including a common terminal and a plurality of individual terminals is used. The switch IC includes a plurality of field-effect transistors (FETs) and connects the common terminal to one of the individual terminals through the on/off operations of the FETs.
In such a switch IC that uses a semiconductor, harmonic signals due to distortion are generated when a high-power high-frequency signal (transmission signal, for example) is input. Such harmonic signals being transmitted to the outside from the common terminal through an antenna causes various problems such as radio wave interference and the like to be generated. In other words, such harmonic signals due to distortion cause degradation of the out-of-band characteristics of the high-frequency switch module.
Hence, the high-frequency circuit disclosed in Japanese Unexamined Patent Application Publication No. 2001-86026 is provided with an LC series resonator that reflects a harmonic signal generated in the switch IC and output to an individual terminal. The LC series resonator is connected between the ground and a signal transmission line connecting the individual terminal of the switch IC to a transmission circuit. As a result, a harmonic signal output from the individual terminal is reflected at a connection point at which the LC series resonator is connected and returns to the switch IC and is transmitted to the common terminal. At this time, by setting, to a predetermined length, the length between the individual terminal and the connection point at which the LC series resonator is connected in the signal transmission line, a harmonic signal output from the common terminal and a harmonic signal from the individual terminal reflected at the connection point at which the LC series resonator is connected and output to the common terminal are made to have opposite phases. With this configuration, a harmonic signal transmitted from the antenna is suppressed.
However, in the existing high-frequency circuit disclosed in Japanese Unexamined Patent Application Publication No. 2001-86026, the phase of a harmonic signal from an individual terminal is adjusted by the length of a signal transmission line which is a distributed-constant line and, hence, the length of the signal transmission line needs to be increased in order to considerably shift the phase. In this case, the shape of a multilayer body forming the signal transmission line is expanded. This makes it difficult to reduce the size of the high-frequency circuit. Further, it is not easy to determine the length and conductor pattern of the signal transmission line for obtaining the optimum amount of phase shift under the constraint of the shape as the multilayer module of the high-frequency circuit. Hence, with the existing configuration disclosed in Japanese Unexamined Patent Application Publication No. 2001-86026, it is difficult to facilitate realization of, and reduction in the size of, a high-frequency circuit which includes a switch IC and has excellent harmonic distortion characteristics and out-of-band characteristics.